This is to ensure the strictest possible rate-limiting of all sizes of packets.QoS, Bandwidth Prioritization, Traffic Shaping and Speed Limit Traffic with larger packet sizes can result in performance somewhat below the configured bandwidth. Optimum rate-limiting occurs with 64-byte packet sizes. (Monitoring shows what traffic is inbound on an interface, and is not affected by "drop" or "forward" decisions.) If monitoring is configured, packets dropped by rate-limiting on a monitored interface are still forwarded to the designated monitor port. Monitoring (mirroring) rate-limited interfaces. For example, ACLs, source-port filters, protocol filters, and multicast filters are all included in bandwidth usage calculations. Configuring a traffic filter on a port does not prevent the switch from including filtered traffic in the bandwidth-use measurement for rate-limiting when it is configured on the same port. In this case, the actual rate for traffic on the rate-limited ports may be lower than configured because the total traffic load requested to the outbound port exceeds the port's bandwidth, and thus some requested traffic may be held off on inbound. In another type of situation, an outbound port can become oversubscribed by traffic received from multiple rate-limited ports.
(This behavior is termed "head-of-line blocking" and is a well-known problem with flow-control.) In this case, the inbound traffic flow does not reach the configured rate and lower priority traffic is not forwarded into the switch fabric from the rate-limited port. For example, in a situation where flow control is configured on a rate-limited port, there can be enough "back pressure" to hold high-priority inbound traffic from the upstream device or application to a rate that is lower than the configured rate limit. Configuring rate-limiting on a port where other features affect port queue behavior (such as flow control) can result in the port not achieving its configured rate-limiting maximum. For outbound rate-limiting, the rate is visible as the percentage of available outbound bandwidth (assuming that the amount of requested traffic to be forwarded is larger than the rate-limit). Instead, this limit is verifiable as the ratio of outbound traffic from an inbound rate-limited port versus the inbound rate. Because inbound rate-limiting is performed on packets during packet-processing, it is not shown via the inbound drop counters. Rate-limiting is visible as an outbound forwarding rate. The hardware will round the actual Kbps rate down to the nearest multiple of 64 Kbps. See Configuring egress per-queue rate-limiting (2920, 3800, and 5400R switches only). NOTE: Rate-limiting on a trunk is allowed for the queues traffic type on the HP 2920 switches. HP Switch(eth-3-5)# rate-limit all in percent 60 HP Switch(config)# int 3-5 rate-limit all in percent 60 For example, either of the following commands configures an inbound rate limit of 60% on ports 3 – 5: You can configure a rate limit from either the global configuration level or from the port context level. However, if this is the desired behavior on the port, HP recommends using the disable command instead of configuring a rate limit of 0. Similarly, if the same port negotiates a 10 Mbps link, then it allows no more than 5 Mbps of inbound traffic.Ĭonfiguring a rate limit of 0 (zero) on a port blocks all traffic on that port. For example, if a 100 Mbps port negotiates a link at 100 Mbps and the inbound rate-limit is configured at 50%, then the traffic flow through that port is limited to no more than 50 Mbps. Percentage limits are based on link speed. A 1-100 Kbps rate-limit is implemented as a limit of 100 Kbps a limit of 100-199 Kbps is also implemented as a limit of 100 Kbps, a limit of 200-299 Kbps is implemented as a limit of 200 Kbps, and so on. For example, if the media speed is 1 Kbps, the value would be 1 Mbps.
Kbps rate-limiting is done in segments of 1% of the lowest corresponding media speed. Rate-limiting does not apply to trunked ports (including meshed ports). The rate-limit icmp command specifies a rate limit on inbound ICMP traffic only (see “ICMP Rate-Limiting”).
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